A paper by Paul W. Abrahams circa 1993, abstract:
Using extended typography, we can design programming languages that utilize modem display and input technologies, thus breaking out of the ASCII straitjacket. We assume that a language has three representations: a visual representation that describes its displayed form, an internal representation defined for each implementation, and an interchange representation, expressed in pure ASCII, that is defined across all implementations. Using extended typography we can use distinctive typefaces to indicate keywords, thus removing the need to reserve them, and can introduce a variety of new symbols more meaningful than those used in most current programming languages. One benefit is the possibility of arbitrary user-defined operators. We can also introduce new kinds of brackets and methods of pairing brackets visually. Extended typography also helps to solve the problems of writing programs in languages other than English.
Sorry I couldn't find a non digital library link, but maybe this would help. I'm surprised no one has looked at this topic again since, at least in academia. Thoughts?